The present invention relates to an image-forming apparatus, such as a copying machine, printer, etc., of an electrophotographic system of forming monochromatic or multi-color images, particularly capable of omitting a cleaning apparatus, to an image-forming process using it, and to a toner used for these apparatus.
Recently, with the rapid propagation of the employment of a computer system, a network system, etc., in offices, the market of copying machines, printers, etc., wherein a monochromatic system has hitherto been the mainstream, is changing to the market wherein a full color system is the mainstream. With the tendency, the requirement for a copying machine, a printer, etc., of an electrophotographic system, which have hitherto been advantageous in the points of the image quality, the speed, etc., has been more and more increased. Particularly, in addition to the increase of the image quality, the increase of the reliability, etc., as well as to small-sizing, light-weighing, the reduction of cost, and the increase of the speed, the ecological counterplans such as energy saving, resource saving, recycling, etc., have been strongly required. Also, to cope with the requirements, the improvements and the new developments of an image-forming process, an image-forming apparatus, and toners used for the system have been carried out.
An image-forming process by an electrophotographic system is generally consisted of an electrostatically charging step of uniformly charging an electrostatic latent image holder surface, a light-exposure step of light-exposing the electrostatic latent image holder surface to form an electrostatic latent image on the surface, a developing step of developing the latent image formed on the electrostatic latent image holder surface using a developer layer formed at a developer holder surface to obtain a toner image, a transfer step of transferring the toner image onto the surface of a transfer material, a fixing step of fixing the toner image on the transfer material, and a cleaning step of removing toners remaining on the electrostatic latent image holder surface in the transfer step.
The toner used for the image-forming process described above is required to have following many fundamental characteristics.
First, in the above-described development step, an appropriate toner charged amount, a charge-retaining property, an environmental stability, etc., are required. Also, in the above-described transfer step, a good transferring property, etc., are required. In the above-described fixing step, a low-temperature fixing property, an offset resistance, etc., are required. Also, in the above-described cleaning step, a good cleaning performance, a stain resistance, etc., are required. In particular, by the recent acceleration of the increase of the image quality, the increase of speed, the formation of color images, etc., the toners have been required to have more and more complicated characteristics.
For example, the image-forming process which recently becomes the mainstream as a full-color copying machine, printer, etc., capable of realizing the formation of images having a high image quality at high speed is an indirect transfer type image-forming process wherein an intermediate transfer material is used for more facilitating matching of the registration at forming color images in the above-described transfer step, and after transferring the toner image on the electrostatic latent image holder surface onto the intermediate transfer material, the toner image is transferred onto a transfer material.
However, in the indirect transfer-type image-forming process, because the transferring times of toners are increased, to realize a high image-quality, an excellent transfer performance is required. Accordingly, for the toners used, a more stabilized charging performance, additives for improving the transfer efficiency, the techniques of controlling the forms and surface structures of the toners, etc., are required.
Also, in the above-described cleaning step, not only from the view points of small-sizing and cost-reducing of the apparatus, and prolonging the life by the abrasion resistance of the electrostatic latent image holder but also from the ecological view points of energy saving, resource saving, the reduction of waste materials, etc., it becomes problems to reduce the amount of the toner remained at transferring and omit the cleaning apparatus.
Particularly, in a full-color image-forming apparatus using four-color developers of yellow, magenta, cyan, and black, the reduction of the amount of toners remained at transferring, omitting the cleaning apparatus, etc., are important problems to be improved.
For the above-described problems, from the view point of generating no waste toners, a cleaner-less system of recovering the toner remained at transferring simultaneously with development without forming a cleaning step is proposed in Japanese Patent Laid-Open Nos. 133573/1984 and 157661/1984.
However, in the above-described cleaner-less system, waste toner is not generated but because foreign matters such as paper powders, etc., are recovered in a developing apparatus together with the remaining toner, there is a problem that the life of the developer is shortened.
On the other hand, a cleaner-less system of not recovering a remained toner is proposed but in the system, there are problems of causing a positive ghost that the toner remained on an electrostatic latent image holder surface is printed and a negative ghost by the light-shielding effect of the toner remained on the electrostatic latent image holder surface.
To avoid the occurrence of the problems of these ghosts, for example, in Japanese Patent Laid-Open No. 114063/1991, a technique of reducing the amount of the toner remained at transferring to 0.35 mg/cm2 or less is proposed and also in Japanese Patent Laid-Open No. 172880/1991, a technique of increasing the transfer efficiency of the toner at transfer step to at least 80% is proposed. In these cleaner-less apparatus, it is required to keep the transfer efficiency of toner at a high level.
As the method of keeping the transfer efficiency of toner at a high level, there are a method of increasing the area of a bias applying portion of a transfer roller proposed in Japanese Patent Laid-Open No. 126872/1981, a method of applying an AC transferring electric field proposed in Japanese Patent Laid-Open Nos. 88770/1983 and 140769/1983, etc.
According to these methods, the transfer efficiency of toner is improved but it is difficult to completely transfer the toner particles directly attached to the electrostatic latent image holder surface and thus these methods are insufficient as a cleaner-less apparatus.
To increase the transfer efficiency of toner, it is important to completely transfer the toner particles directly attached to the electrostatic latent image holder surface and for the purpose, it is effective to lower the adhesive force between the toner particles and the electrostatic latent image holder surface. As such a method, there is a method wherein releasing fine particles such as silica, etc., are incorporated in a developer and the fine particles are placed between toners and the electrostatic latent image holder surface to lower the adhesive force between the toner and the electrostatic latent image holder surface, whereby the transfer efficiency of the toner is increased as proposed by Japanese Patent Laid-Open Nos. 1870/1990, 81053/1990, 18671/1990, 118672/1990, and 157766/1990.
However, in these methods, because to increase the transfer efficiency, it is necessary to highly establish the covering ratio of the toner surfaces by the fine particles, it is required to add a large amount of the fine particles. Thereby, there occur the problems that the charging property of the toner is deteriorated and the liberated fine particles are liable to attach to the electrostatic latent image holder to cause problems of filming, the hindrance of the fixing property, etc.
Also, because by a strong stress causing by stirring in the developing apparatus, a layer regulation, etc., embedding, releasing, etc., of the fine particles occur, there is a problem that the high transfer efficiency is kept for a long time.
Also, because when silica fine particles are used as the fine particles, the transfer efficiency is improved but the environmental reliance is large, there is a problem that under a low-temperature low-humidity environment, an image density unevenness occurs and under a high-temperature high-humidity environment, a fog, etc., are liable to occur.
As a method of solving the above-described problems and obtaining a high transfer efficiency of toner, the present applicant, etc., previously proposed a method of attaching fine particles onto the electrostatic latent image holder surface and developing an electrostatic latent image formed thereon by a toner in Japanese Patent Laid-Open No. 212010/1997. Also, the present applicant, etc., previously proposed a method of attaching fine particles onto the electrostatic latent image holder surface and also externally adding fine particles onto the surfaces of spherical toners in Japanese Patent Laid-Open No. 52610/1999.
According to these methods, because the transfer efficiency of the toner is greatly improved, image defects such as ghosts and fog, etc., by the toner remained at transferring do not occur for a long period of time.
However, because in these methods, a step of uniformly attaching the fine particles on the electrostatic latent image holder surface before developing the latent image formed on the electrostatic latent image holder surface by the toner, from the view points of simplifying and small-sizing the image-forming apparatus, increasing the image-forming speed, increasing the productivity of the electrostatic latent image holder, reducing the cost, etc., these methods are not always satisfactory and thus a further improvement has been desired.
Also, in these methods, it is considered to be important to always keep the amount of the fine particles attaching to the electrostatic latent image holder surface and the dispersibility of the fine particles at the optimum states, but because the amount of the fine particles supplied from the toner to the electrostatic latent image holder surface and attaching the surface in the fine particles attached to the electrostatic latent image holder surface differs according to the developing amount with the toner, the amount thereof differs by the kind of images, the number of sheets, etc., to be printed, an image quality hindrance caused thereby sometimes occurs.
That is, because the attaching amount of the fine particles onto the electrostatic latent image holder surface is changed by the change of the number of the printed sheets, and also according to the difference in image densities, a difference of the attached amount of the fine particles between an imaged portion and a non-imaged portion occurs, the image defects such as the change of image density, the density unevenness, ghosts, etc., considered to be caused by the difference of the surface potential after charging and light exposing corresponding to the attached amount of the fine particles on the electrostatic latent image holder surface or by the differences in the development efficiencies, the transferring efficiencies, etc., sometimes occur.
Also, actually, in these methods, the use of fine particles of relatively small particle sizes the surfaces of which were subjected to a hydrophobic treatment is liable to be attached to electrostatic latent image holder surface and shows a larger effect of improving the transfer efficiency, but because the fine particles of relatively small particle sizes subjected to a hydrophobic treatment show a very strong aggregating property, it is very difficult to uniformly attach the fine particles onto the electrostatic latent image holder surface in the state of near the primary particle size in, as a matter of course, the initial supply of the fine particles and in the supplying course of the fine particles from the toner, and it sometimes happens to become the state of attaching nonuniform fine particles containing many aggregated fine particles.
Because in such a case, the difference in the attached amounts of the fine particles by the difference in the above-described developing amounts is liable to become large, in addition to the problems of causing the image density change, the density unevenness, ghosts, etc., there are problems that the image quality defects such as white spots, black spots, etc., by the aggregated fine particles occur.
Such a problem of attaching materials onto the electrostatic latent image holder surface is an important problem not only from the view point of the improvement of the image quality reliance but also from the view points of prolonging the life of the electrostatic latent image holder, lowering the cost thereof, energy saving, resource saving, etc.
That is, in an image-forming apparatus equipped with a cleaning apparatus such as an elastic blade, etc., to the electrostatic latent image holder, which becomes the mainstream at present, the life of the electrostatic latent image holder is almost determined by the abrasion, scratches, etc., by the blade but in the image-forming apparatus of a cleaner-less system, the electrostatic latent image holder surface is not abraded but it is considered that the life of the electrostatic latent image holder is determined by the image defects caused by the attached materials such as the above-described fine particles in the toner, the toners, the toner composition, a carrier, a carrier coating agent composition, and other foreign matters, etc. Particularly, by recent small-sizing of the apparatus, because in the case of using the electrostatic latent image holder having a small diameter, etc., the usable electrostatic latent image holder surface area becomes smaller, the problem of shortening the life of the electrostatic latent image holder by these attached materials is the important problem to be improved.
Also, in the case of not using a cleaning apparatus of removing the toner remaining on the electrostatic latent image holder surface, the toner, the fine particles, etc., attached to the electrostatic latent image holder surface stain the members such as the charging device, etc., in contact with the electrostatic latent image holder, which causes the charging failure, etc.
Accordingly, from these view points, the control of the supplying amount of the fine particles is the important improving problem. As described above, in order to supply hardwares, toners, etc., capable of satisfying the recent high market requirements of the formation of color images of high image quality, the increasing the image-forming speed, the high reliance, small-sizing and cost-reducing of the apparatus, and coping with the ecology, there yet exist problems to be solved.
The present invention has been made for solving the above-described various problems in the techniques of related art and for attaining the following features and provides an image-forming process capable of obtaining images having stabilized image quality giving a reduced amount of toners to be recovered and wasted without causing the image quality defects such as lowering of density, a density unevenness, ghosts, fog, etc., for a long period of time by keeping a high toner transfer efficiency for a long period of time, provides toners used for the image-forming process, and also provides an image-forming apparatus used for the process.
The present invention is as follows.
That is, a 1st aspect of the invention is an image-forming process of forming images on the surface of a transfer material including a developing step of obtaining a toner image by developing an electrostatic latent image on an electrostatic latent image holder surface using a layer of a developer containing at least a toner on the surface of a developer-holding member, a transfer step of transferring the toner image onto the surface of a transfer material, and a fixing step of fixing the toner image on the surface of the transfer material, wherein
the toner contains at least toner particles and inorganic fine particles,
the inorganic fine particles transfer from the toner to the electrostatic latent image holder surface and attach thereto and the attached amount of the inorganic fine particles attached to the electrostatic latent image holder surface is from about 1 to 20% by the average occupied area ratio (CAV) in the electrostatic latent image holder surface, and
the difference (CMAXxe2x88x92CMIN) of the maximum occupied area ratio and the minimum occupied area ratio of the attached inorganic fine particles in the electrostatic latent image holder surface is not larger than about 5%.
A 2nd aspect of the invention is an image-forming process of forming an images on the surface of a transfer material including a developing step of obtaining a toner image by developing an electrostatic latent image on an electrostatic latent image holder surface using a layer of a developer containing at least a toner on the surface of a developer-holding member, a 1st transfer step of transferring the toner image onto the surface of an intermediate transfer member, a 2nd transfer step of transferring the toner image on the surface of the intermediate transfer member on to the surface of a 2nd transfer material, and a fixing step of fixing the toner image on the surface of the transfer material, wherein
the toner contains at least toner particles and inorganic fine particles,
the inorganic fine particles transfer from the toner to the electrostatic latent image holder surface and attach thereto and the attached amount of the inorganic fine particles attached to the electrostatic latent image holder surface is from about 1 to 20% by the average occupied area ratio (CAV) in the electrostatic latent image holder surface, and
the difference (CMAXxe2x88x92CMIN) of the maximum occupied area ratio and the minimum occupied area ratio of the attached inorganic fine particles in the electrostatic latent image holder surface is not larger than about 5%.
In the image-forming process of the above-described 1st aspect or 2nd aspect, it is preferred that the ratio (a2/a1) of the average primary particle size (volume average primary particle size) of the inorganic fine particles contained in the toner (hereinafter, is sometimes referred to as simply xe2x80x9caverage primary particle sizexe2x80x9d) (a1) and the average aggregated particle size (volume average aggregated particle size) of the transferred and attached inorganic fine particles (hereinafter, is sometimes referred to as simply xe2x80x9caverage aggregated particle sizexe2x80x9d) (a2) is not larger than about 5.
A 3rd aspect of the invention is a toner used for the image-forming process of the above-described aspect 1 or 2.
In the toner of the 3rd aspect, it is preferred that the inorganic fine particles in the toner are subjected to a surface hydrophobic treatment and the average primary particle size (a1) thereof is from about 10 to 50 nm.
Also, in the toner of the 3rd aspect, it is preferred that the ratio (C/C0) of the calculated covering ratio (C0) of the inorganic fine particles in the surfaces of the toner particles and the practically measured covering ratio (c) is at least about 0.6.
Furthermore, in the toner of the 3rd aspect, it is preferred that the inorganic fine particles are attached to the toner particles, and in the inorganic fine particles attached thereto, the ratio of the weakly attached inorganic fine particles is not larger than about 40% by weight, and the ratio of the strongly attached inorganic fine particles is not larger than about 80% by weight.
Also, in the toner of the 3rd aspect, it is preferred that the inorganic fine particles are titanium oxide fine particles having a volume resistivity of from about 1xc3x971010 to 1xc3x971014 xcexa9cm.
Furthermore, in the toner of the aspect 3, it is preferred that the calculated covering ratio (C0) of the inorganic fine particles in the surfaces of the toner particles is from about 10 to 50%.
Also, in the toner of the 3rd aspect, it is preferred that the sphericity of the toner particle is not more than about 130.
Still further, in the toner of the 3rd aspect, it is preferred that the average primary particle size thereof is larger than the average primary particle size of the inorganic fine particles attached to the electrostatic latent image holder surface, and at least one kind of the spherical fine particles of from about 30 to 200 nm are attached to the surfaces of the toner particles.
Also, in the toner of the 3rd aspect, it is preferred that the spherical fine particles are silica fine particles subjected to a surface hydrophobic treatment.
A 4th aspect of the invention is an image-forming apparatus of forming an image on the surface of a transfer material equipped with a developing unit of obtaining a toner image by developing an electrostatic latent image on an electrostatic latent image holder surface using a layer of a developer containing at least a toner on the surface of a developer-holding member, a transfer unit of transferring the toner image onto the surface of a transfer material, and a fixing unit of fixing the toner image on the surface of the transfer material, wherein
the toner contains at least toner particles and inorganic fine particles,
the inorganic fine particles transfer from the toner to the electrostatic latent image holder surface and attach thereto and the attached amount of the inorganic fine particles attached to the electrostatic latent image holder surface is from about 1 to 20% by the average occupied area ratio (CAV) in the electrostatic latent image holder surface, and
the difference (CMAXxe2x88x92CMIN) of the maximum occupied area ratio and the minimum occupied area ratio of the attached inorganic fine particles in the electrostatic latent image holder surface is not larger than about 5%.
A 5th aspect of the invention is an image-forming apparatus of forming an image on the surface of a transfer material equipped with a developing unit of obtaining a toner image by developing an electrostatic latent image on an electrostatic latent image holder surface using a layer of a developer containing at least a toner on the surface of a developer-holding member, a 1st transfer unit of transferring the toner image onto the surface of an intermediate transfer member, a 2nd transfer unit of transferring the toner image on the surface of the intermediate transfer member on to the surface of a second transfer material, and a fixing unit of fixing the toner image on the surface of the transfer material, wherein
the toner contains at least toner particles and inorganic fine particles,
the inorganic fine particles transfer from the toner to the electrostatic latent image holder surface and attach thereto and the attached amount of the inorganic fine particles attached to the electrostatic latent image holder surface is from about 1 to 20% by the average occupied area ratio (CAV) in the electrostatic latent image holder surface, and the difference (CMAXxe2x88x92CMIN) of the maximum occupied area ratio and the minimum occupied area ratio of the attached inorganic fine particles in the electrostatic latent image holder surface is not larger than about 5%.
In the image-forming apparatus of the 4th or 5th aspect, it is preferred that the ratio (a2/a1) of the average primary particle size of the inorganic fine particles contained in the toner (a1) and the average aggregated particle size of the transferred and attached inorganic fine particles (a2) is not larger than about 5.
In the image-forming apparatus of the 4th or 5th aspect, it is preferred that the inorganic fine particles are subjected to a surface hydrophobic treatment, and the average primary particle size (a1) is from 10 to 50 nm.
Also, in the image-forming apparatus of the 4th or 5th aspect, it is preferred that the inorganic fine particles are titanium oxide fine particles having a volume resistivity of from about 1xc3x971010 to 1xc3x971014 xcexa9cm.